Device for sensing the operative status of electrical equipment

ABSTRACT

The operative status of an electrical apparatus unit such as a television receiver, incorporating an AC-DC converter, and drawing a substantial amount of current is sensed while differentiating from the usage of a lower amount of current, as when operating in a standby mode. The sensor distinguishes between the standby current waveform and a distinctly different current waveform generated when the AC-DC converter draws current in the mode in which full power is on. The sensor incorporates a reference current detector responsive to the mean of the absolute value of alternating current flowing through a power line to the electrical unit, and a peak value current detector responsive to the peak value of the periodic signal on the power line. A comparator circuit receives outputs from both detectors, and provides an output signal when the ratio therebetween is in excess of a predetermined value, this condition only applying when the AC-DC converter is operative. The comparator may comprise a differential amplifier which periodically triggers a pulse generator to maintain a selected signal level and activate a relay as long as the selected proportionality exists between the peak and mean values of the AC power signal.

BACKGROUND OF THE INVENTION

This invention relates to a device for sensing the operative status ofan electrical apparatus unit which is provided with an AC-DC converter,the sensor being adapted to distinguish between conditions of operationand non-operation (including a standby condition).

In prior art devices, the operating condition of an electrical apparatusunit has been sensed by detecting the presence of an electric currentsupplied to the unit or by detecting whether an amount of an electriccurrent is in excess of a reference value or not. However, differentelectrical apparatus units are different in their electric currentconsumption according to classes and conditions of use thereof. Further,various apparatuses are each different in operating electric current andnon-operating electric current modes, such as, for example, those thatuse a small flow of electric current in order to place the apparatus ina standby condition (for example, a television set having a preheatfunction). For example, there is one type of electrical apparatus whichconsumes only a minute amount of electric current even though it is inan operating condition, while there are others which consume an electriccurrent more than the aforesaid minute amount of electric current tomaintain the apparatus in a standby condition. Therefore, conventionalsensing devices, which detect the operation or non-operation ofelectrical apparatus merely from the presence or magnitude or an amountof electric current, cannot be employed with devices for which thereference values must be adjusted or in which partial power consumptionmust be distinguished from normal operation.

SUMMARY OF THE INVENTION

The present invention provides an improved system for distinguishingbetween different operative states of electrical apparatus devices,based upon the conception that such devices when provided with an AC-DCconverter produce a difference in power source electric current waveformbetween the operating condition and the non-operating condition. In aparticular example of a system in accordance with the invention, thedifferences in such waveform are determined by comparing an average ormean waveform amplitude with the peak waveform signal, as in adifferential amplifier, to provide an output signal only when the ratiois in excess of a predetermined amount. Further, the pulse output signalderived from comparison of successive half waves of the power sourcesignal may be utilized to generate a momentary signal to actuate a pulsegenerator which charges an integrating circuit controlling an associatedrelay so as to provide an output signal as long as power usagecontinues, without erroneous response to transient noise spikes.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention may be had by reference to thefollowing description, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram showing one example of a device for sensing anoperating condition of electrical apparatus in accordance with thepresent invention;

FIG. 2 is a graphical representation of electric current waveforms usedin explaining the operation of the device of FIG. 1; and

FIG. 3 is a schematic diagram of a specific circuit in accordance withthe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram showing one embodiment of a device for sensingan operating condition of electrical apparatus in accordance with thepresent invention. The device comprises an AC power source line 1 forthe electrical apparatus 2, an electric current detector 3 for detectingthe electric current flowing through the power source line 1, areference electric current detector 4 for obtaining a mean value ofelectric current detected by the electric current detector 3, a peakvalue electric current detector 5 for obtaining a peak value of electriccurrent detected by the electric current detector 3, and a comparator 6for comparing an output of the reference electric current detector 4with an output of the peak electric current detector 5.

In the arrangement as described above, the electrical apparatus 2obtains a DC current from an AC current supplied from the power sourceline 1 through an incorporated AC-DC converter (for example, diodebridge rectifier and smoothing condenser), the DC current being suppliedto the internal circuits of the apparatus. Since the electric currentflowing in the power source line 1 is to supply the electric powerconsumed due to operation of the electrical apparatus 2, the electriccurrent waveform thereof is a pulse electric current flowing due toconduction of the rectifying diodes in the vicinity of the peak of thesinusoidal electric current flowing through the quasi-resistive portionsof the apparatus, as shown in FIG. 2(a). Therefore, when the electricalapparatus 2 is in a condition of normal operation, the electric currentdetector 3 will detect an electric current having a waveform shown inFIG. 2(a). From this current, an output having a waveform shown at a inFIG. 2(b) is obtained in the peak value electric current detector 5 andan output having a waveform shown at b in FIG. 2(b) is obtained in thereference electric current detector 4, whereby an output of thecomparator 6 is reversed by the pulse electric current. Both waveformsrepresent absolute values (i.e. unidirectional signals) of the appliedpower signal. In contrast, when the electrical apparatus 2 is in acondition of non-operation or in a condition of stand-by, the output ofthe peak value electric current detector 5 is a sine wave electriccurrent without a pulse electric current and is lower in level than theoutput of the reference electric current detector 4 so that the outputof the comparator 6 is not reversed. As a result, the condition ofoperation or non-operation (including stand-by condition) of theelectrical apparatus 2 may be sensed according to an output condition ofthe comparator 6. Thus, the output of the reference electric currentdetector 4, which serves as a reference of comparison, may be variedaccording to the electric current consumed by the electrical apparatus 2connected to thereby obtain a reference electric current value inconformity with the electrical apparatus 2 so as to be able to securelysense the operation and non-operation of the electrical apparatus asdesired.

FIG. 3 is a circuit representation showing an embodiment of a device forsensing an operating condition of electrical apparatus according to thepresent invention, in which dotted line blocks indicate correspondingparts in FIG. 1. In this figure, the electric current detector 3comprises an electric current detector transformer 3A of which theprimary is connected in series to the power source line 1, and thereference electric current detector 4 comprises an arrangement in whichsecondary outputs of the electric current detector transformer 3A aresubjected to full-wave rectification by diodes 4A and 4B and smoothed byresistor 4C and capacitor 4D. It should be noted that resistor 4Econstitutes a division circuit in cooperation with resistor 4C and alsodischarges an electric charge from capacitor 4D. Next, the peak valueelectric current detector 5 comprises an arrangement in which secondaryoutputs of the electric current detector transformer 3A are subjected tofull-wave rectification by diodes 5A and 5B and divided by resistors 5Cand 5D connected in series with each other. The comparator 6 comprises adifferential amplifier composed of transistors 6A, 6B and the like. InFIG. 3, the reference numeral 7 designates a unistable multivibratoradapted to feed pulses of a predetermined width in response to a pulseoutput from the comparator 6, a capacitor 8 to smooth the output of theunistable multivibrator 7, a switch circuit 9 which is turned ON when acharging voltage of the capacitor 8 exceeds a predetermined level(determined by the ON voltage of Zener diode and transistor), and arelay 10 excited when the switch circuit 9 is turned ON.

In the arrangement as described above, the ratio of voltage divisionbetween resistors 5C and 5D and the ratio of voltage division betweenresistors 4C and 4E are set so that when the electrical apparatus 2 isin a condition of non-operation, the transistor 6B is maintained in theOFF condition. That is, they are set in such a way that if the electriccurrent flowing through the power source line 1 is a sine wave, the DCoutput of the reference electric current detector 4 is always higher inlevel than the output having a full-wave rectification waveform of thepeak value electric current detector 5. With such a setting procedure,only when the pulse electric current is superposed on the currentflowing in the power source line 1, the transistor 6B is turned ON andthe unistable multivibrator 7 is triggered to charge the capacitor 8.Several cycles of such operation are repeated until the charging voltageof the capacitor 8 is reached, and as a consequence the switch circuit 9is turned ON to activate the relay 10. This activation of relay 10indicates that the electrical apparatus 2 is in a condition ofoperation. The capacitor 8 is provided to prevent the sensor device frombeing erroneously operated when an unexpected noise pulse is inducedinto the power source line 1.

While the peak value electric current detector and mean value electriccurrent detector with the detected electric current subjected tofull-wave rectification have been illustrated in the above-mentionedembodiment, it is to be understood that half-wave rectification may alsobe employed.

As is obvious from the foregoing, the present invention provides adevice for sensing an operating condition of electrical apparatus,wherein utilization of a difference in power source electric currentwaveform between the operating condition and the non-operating conditionof electrical apparatus is made to compare a mean value with a peakvalue of the power source electric current thereby sensing the operationand non-operation of the electrical apparatus. Accordingly, a deviceaccording to the invention is a sensor device which is capable ofautomatically obtaining a compared reference value in conformity with aconsumption current of electrical apparatus, and capable of securelysensing the operation and non-operation of electrical apparatusirrespective of magnitude of the consumption current thereof.

What is claimed is:
 1. A device for sensing the energization conditionof an electrical apparatus including an AC-DC converter circuit from atleast one power line for the apparatus, comprising:first amplitudedetector means responsive to the current in the power line forgenerating a mean value signal indicative of the mean value of saidcurrent; second amplitude detector means responsive to the current inthe power line for generating a peak value signal indicative of the peakvalue of said current, the peak value signal being substantially greaterin a first mode when the AC-DC converter is utilized than in a secondmode when the converter is not utilized; and comparator means responsiveto the mean value signal and peak value signal for indicating theexistence of an energized condition for the electrical apparatus whenthere is greater than a selected ratio between the peak value and meanvalue signals.
 2. The invention as set forth in claim 1 above, whereinsaid device further comprises means in series circuit with the powerline for the electrical apparatus for detecting the current waveform,wherein said first amplitude detector means provides an integratedsignal and said second amplitude detector means provides a signalvarying with the absolute value of the current waveform, and whereinsaid device further comprises means responsive to said comparator meansfor providing a steady state indication of the energization condition ofthe electrical apparatus.
 3. A device for sensing the energizationcondition of an electrical apparatus including an AC-DC convertercircuit from at least one power line to the apparatus, comprising:meansin series circuit with the power line for the electrical apparatus fordetecting the current waveform of current therein; first amplitudedetector means responsive to the detected current waveform, the firstamplitude detector means including a first terminal, rectifier means,capacitor means and first voltage divider means coupled to provide tothe first terminal an integrated mean absolute value signal varying withthe integrated mean absolute value of the detected current waveform; asecond amplitude detector means responsive to the detected currentwaveform, the second amplitude detector means including a secondterminal, rectifier means, and second voltage divider means coupled toprovide to the second terminal a peak value signal varying with the peakabsolute value of the detected current waveform; comparator meansresponsive to the mean value signal and peak value signal for indicatingthe existence of an energized condition for the electrical apparatuswhen there is greater than a selected ratio between the peak value andmean value signals, the comparator means including differentialamplifier means coupled to receive signals from the first and secondterminals and to provide an output signal when the voltage at the secondterminal is greater than that at the first terminal, the ratio ofvoltages at the second and first terminals being selected to provide anoutput signal from said differential amplifier means only when animpulse peak signal arising from operation of the AC-DC converter issuperposed on the power line signals; and means responsive to saidcomparator means for providing a steady state indication of theenergization condition of the electrical apparatus.
 4. The invention asset forth in claim 3 above, including in addition pulse generator meansresponsive to the output from said differential comparator means,integrating means coupled to integrate the output signal from the pulsegenerator means, and switching signal means responsive to the outputlevel of the integrating means for providing an output signal when theoutput level of the integrating means is in excess of a selectedthreshold level.
 5. The invention as set forth in claim 3 above, whereinsaid first and second voltage divider means each comprise a pair ofresistor means having a midpoint output terminal therebetween, andwherein said differential amplifier means has first and second inputscoupled to said midpoint terminals of said first and second voltagedivider means respectively, and wherein said differential amplifiermeans includes an output transistor which is arranged to be conductivewhen the selected ratio between the peak absolute value signal and themean absolute value signal exists.
 6. A system for distinguishing thefull energization condition of an electrical unit including an AC-DCconverter from a standby condition in which alternating current is drawnwithout activation of the AC-DC converter to superpose a pulse peak onthe alternating current waveform, comprising:means coupled in circuitwith the electrical unit for sensing the current waveform thereat; meansresponsive to the ratio between the peak level of the absolute value ofthe sensed current and the mean level of the absolute value of thesensed current for providing a pulse output for each half-cycle in whichgreater than a selected ratio exists; means responsive to the pulseoutputs from the ratio responsive means for generating a control voltagewhose amplitude is responsive to the number of pulse outputs received ina predetermined time; and means responsive to the control voltage forgenerating a steady state output signal when the control voltage is inexcess of a predetermined level.
 7. The invention as set forth in claim6 above, wherein said ratio responsive means comprises a unistablemultivibrator coupled to charge an integrating capacitor to provide thecontrol voltage.
 8. The invention as set forth in claim 7 above, whereinsaid means for generating a control voltage comprises switch meanscoupled to be conductive in response to a selected level of controlvoltage, and relay means responsive to conduction of said switch means.